v4l2codecs: allocator: Keep dmabuf mapped
DMABuf allocator already implements DMABuf Sync, meaning that doing mmap/munmap (unless the mode have changed) is not requires. In fact, on systems with IOMMU it makes the kernel redo the mmu table which is visible in the CPU usage.
This change reduces CPU usage when decoding bbb_sunflower_2160p_60fps_normal.mp4 on RK3399 SoC from over 30% to around 15%.
cc @dwlsalmeida
Edited by Nicolas Dufresne